Check the unstable process of the zero point electromagnetic flowmeter. First, according to the process, think about the initial pace of investigation and discrimination, and then carefully examine and try to remove the problem. The criteria for the inspection items listed in the process are the first ones that can be observed or interrogated to understand that there is no need for a large operation, that is, it is difficult to press the past on-site inspection experience, and the frequency of presentation is higher and the probability of higher probability may be higher in the future. Check the sequential requests you need. If the initial steps are confirmed to be the cause of the latter problems, it can be carefully examined early.
The pipe is not filled with liquid or the bubble in the liquid objectively means that there is no activity in the flow sensor and there is actually a small amount of activity. The main reason for this type of fault is that the shut-off valve of the pipeline is poorly sealed, and the small amount of leakage detected by the electromagnetic flowmeter is misinterpreted as zero change or zero instability.
The use of valves for long periods of time or liquid contamination to seal the valve is often encountered, especially for large valves. Another common reason is that the flow meter has a number of branches in addition to the main pipe, forgotten or neglected that the valves of these branches are closed. Sometimes it is difficult to confirm that the management system is inactive at the scene. At this point, you can check if there is any leakage.
The conductivity of the liquid changes or is uneven, and the zero point changes when it is stationary, and the output is shaken when it is active. Therefore, the flowmeter should be located away from the point of injection of the liquid or downstream of the chemical section of the pipeline, and the flow sensor should be installed upstream of these places. If the liquid contains a solid phase, or impurities accumulate on the inner wall of the flowmeter, or foul on the inner wall of the flowmeter, or the electrode is contaminated by grease, etc., there may be zero variation.
Since the scale of the inner wall and the level of electrode contamination are not exactly the same and symmetrical, the equilibrium of the initial zero setting is destroyed. The positive measure is to eliminate the pollution and accumulation of scale; if the zero is not changed, try to re-zero.
Changes in the state of the power device near the flow sensor (such as increased leakage current) constitute a change in the ground potential, which also causes a zero point change in the electromagnetic flowmeter. The external disturbances such as the stray current of the pipeline mainly depend on the good grounding maintenance of the electromagnetic flowmeter. Usually, the grounding resistance is less than 10, and it should not be grounded with other motor and electrical appliances. Sometimes the environmental conditions are good, the electromagnetic flowmeter can work normally without grounding, but once the good environment does not exist, the instrument will be faulty, and then checking will bring a lot of trouble.
Check the flow chart. Insulation landing of the signal loop will constitute zero instability. The main reason for the signal loop insulation fall is caused by the insulation drop of the electrode part, but it can't sweep the signal cable and its terminal block insulation drop or damage. Because the site environment is very cruel sometimes, the instrument cover and the wire joint are not neglected. Be cautious, overflowing with moisture mist or dust and dust into the instrument junction box or cable maintenance layer to make the insulation fall.
The signal loop insulation resistance check is stopped by the cable side and the flow sensor respectively, and is tested with a megger. Since the signal cable is easy to detect, it can be done first.
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